CHARACTERISTICS OF WATER 73 



table and allow it to stand for several minutes. Insert a lighted 

 splinter. Why is not the hydrogen still present? 



Draw out a glass tube so that the bore will be about as large as 

 the point of a pencil and insert it in the rubber delivery tube. Pour 

 more acid into the bottle and after this has been working for several 

 minutes touch a lighted match to the glass tip of the rubber delivery 

 tube. A jet of burning hydrogen will be formed. Hold a cold dry 

 beaker over this burning jet. Water drops will collect in the beaker. 

 The hydrogen is combining with the oxygen of the air and water is 

 being formed. 



Pure water is a chemical compound of two gases, hy- 

 drogen and oxygen. The oxygen we have always been 

 familiar with, as it makes up about one fifth of the air by 

 which we are surrounded. The hydrogen was prepared 

 in the previous experiment. It is a colorless transparent 

 gas, the lightest of all substances, and must be handled 

 carefully. If it is mixed with oxygen or air and the 

 mixture ignited, it explodes with much violence, forming 

 water. 



Experiment 37. Fill a small beaker with fresh water. Heat it 

 slowly. Bubbles collect on the bottom and sides. When the water 

 becomes cold these bubbles do not disappear. If they were steam, 

 they would change back to water. What are they? Where did they 

 come from? Does water contain dissolved air? How can water 

 animals that do not come to the surface obtain the air they need ? 



Experiment 38. Put a piece of ice in water. What part of its 

 volume sinks below the surface of the water? Is it heavier or lighter 

 than water ? From Experiment 24 do you conclude that cold water 

 is heavier or lighter than warm water? 



The water that we usually see has air and other sub- 

 stances dissolved in it, for water is the greatest solvent 

 known. Another property of water which is very im- 

 portant is its practical incompressibility. No matter how 

 much pressure may be put upon water its volume is little 

 decreased and its density little changed. So it happens 



